W. N. Benson — Origin of Serpentine. 723 



Paringu serpentine, masses of diopside, diallage, with 

 grossularite, vesnvianite, fassaite, clinozoisite, lotrite (a 

 form of prehnite), clinochlore, apatite, ilmenite, rutile 

 and sphene. He concluded that the more coarsely gran- 

 nlitic masses, with an appearance like that of saussurite- 

 gabbro, were indeed an altered form of gabbro, but that 

 some hornstones of similar mineral composition were 

 altered inclusions of chloritic calc-schist. The writer has 

 found that in the serpentine of the Bingara region, 

 N. S. W., there are numerous masses of pale green or 

 white grossularite rocks, and that every stage can be 

 noted in the change from gabbro with 15-8% CaO and a 

 specific gravity of 2-93 to a grossularite rock with 33-3% 

 CaO and a specific gravity of 342. The development of 

 prehnite is often quite considerable. If it be, as seems 

 probable, that the addition of lime was obtained during 

 the process of serpentinization, we could here conclude 

 from this mineralogical change that the peridotite had 

 not been hydrated at the time of the intrusion of the gab- 

 bro, just as in the case of the Lizard rocks. The Tasma- 

 nian lime-silicate rocks are ascribed by Ward (1911) and 

 Waterhouse (1916) to the " chemical reaction of the 

 emanations from the acid magma-hearths upon the walls 

 of the fissures that traverse the basic-rocks. " 



Steinmann (1908), while elaborating his view that 

 nephrite masses are formed from originally continuous 

 dikes of websterite, broken and metamorphosed during 

 the serpentinization and expansion of the including 

 masses of peridotite, states that the copper veins in the 

 serpentine have also been dislocated by the expansion, 

 the effects of the pressure varying so much locally that 

 it can hardly be the result of orogenic movement alone. 

 He adds that wherever the evidence is clear one can 

 prove that the peridotite was still anhydrous when it was 

 invaded by gabbro, indeed sometimes it seems probable 

 that it was still hot. From this he infers that the pro- 

 cesses of serpentinization, and of the nephritization and 

 saus^suritization connected therewith, commenced only 

 after the vulcanicity had been so far exhausted that ore- 

 formation had occurred, but, on the other hand, that the 

 processes had been completed before the last stage of the 

 orogenic epoch that commenced with the intrusion of the 

 peridotite, and ended with great overthrustings. Fin- 

 layson (1909), referring to the serpentines and peri- 

 dotites of Dun Mt., N. Z., in which there occur sulphidic 



